Question 1

Which statement best describes molecular recognition in biochemistry?

Accepted Answer

It is the ability for certain molecules to bind to one another in the face of many alternative structures, forming complexes with well-defined three-dimensional shapes.

Question 2

Myoglobin and hemoglobin both bind heme. What is the primary function of myoglobin in muscle tissue?

Accepted Answer

To bind and store oxygen for use when muscles expand energy.

Question 3

Consider the equilibrium $R + L \rightleftharpoons RL$. What does the percentage of RL complex formed depend on?

Accepted Answer

The concentrations of both R and L.

Question 4

The dissociation constant $K_d$ for a receptor-ligand interaction is defined as:

Accepted Answer

$K_d = \frac{[R][L]}{[RL]}$

Question 5

Estradiol binds to the estrogen receptor with an $L_{50}$ of approximately 1 nM. What does $L_{50}$ represent in this context?

Accepted Answer

The concentration of ligand at which half of the receptors are bound to ligand and half are free.

Question 6

Why does the estrogen receptor discriminate between estradiol and testosterone?

Accepted Answer

Estradiol is aromatic and planar, fitting neatly into the receptor's binding pocket, while testosterone is not.

Question 7

Which feature of myoglobin allows it to discriminate between oxygen and carbon monoxide?

Accepted Answer

The presence of a distal histidine that stabilizes bound oxygen through hydrogen bonding.

Question 8

Hemoglobin exhibits cooperative binding of oxygen. What does this mean?

Accepted Answer

Binding of oxygen at one site increases the affinity at other sites.

Question 9

Which of the following best explains the effect of 2,3-bisphosphoglycerate (2,3-BPG) on hemoglobin?

Accepted Answer

2,3-BPG stabilizes the T state and facilitates the release of oxygen.

Question 10

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin. What is the molecular basis for this difference?

Accepted Answer

Fetal hemoglobin has a lower affinity for 2,3-BPG, resulting in higher oxygen affinity.

Question 11

The Bohr effect describes how hemoglobin's oxygen affinity is regulated by which factors?

Accepted Answer

Carbon dioxide and hydrogen ion concentration (pH).

Question 12

What is the effect of lowering pH on hemoglobin's oxygen affinity?

Accepted Answer

It decreases oxygen affinity by stabilizing the T state.

Question 13

Carbon dioxide stabilizes deoxyhemoglobin by forming carbamate groups. What is the consequence of this modification?

Accepted Answer

It stabilizes the T state, favoring oxygen release.

Question 14

A patient is exposed to carbon monoxide (CO). Why is CO poisoning dangerous in terms of hemoglobin function?

Accepted Answer

CO binds to hemoglobin's heme iron, competing with oxygen and preventing oxygen transport.

Question 15

Sickle-cell anemia is caused by a mutation in the hemoglobin gene. What is the specific amino acid substitution responsible for this disease?

Accepted Answer

Glutamate is replaced by valine at position 6 of the beta chain.

Question 16

Which structural change occurs in hemoglobin upon oxygen binding that drives cooperativity?

Accepted Answer

The proximal histidine and its associated alpha helix move, transmitting the change to the interface between dimers.

Question 17

Which model of hemoglobin cooperativity states that the entire tetramer exists only in either the T state or the R state, and ligand binding shifts the equilibrium between these states?

Accepted Answer

The concerted model.

Question 18

Given the forward rate constant $k_{on}$ and the reverse rate constant $k_{off}$ for a receptor-ligand interaction, how is the equilibrium dissociation constant $K_d$ calculated?

Accepted Answer

$K_d = k_{off} / k_{on}$

Question 19

A drug binds to its receptor with a very low $K_d$. What does this indicate about the drug's binding affinity?

Accepted Answer

The drug binds very tightly to the receptor.

Binding and Molecular Recognition: Protein Structure, Ligand Interactions, and Oxygen Transport

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